Deformable Conductors and Related Sensors, Antennas and Multiplexed Systems

ABSTRACT

A conducting shear thinning gel composition and methods of making such a composition are disclosed. The conducting shear thinning gel composition includes a mixture of a eutectic gallium alloy and gallium oxide, wherein the mixture of eutectic gallium alloy and gallium oxide has a weight percentage (wt %) of between about 59.9% and about 99.9% eutectic gallium alloy, and a wt % of between about 0.1% and about 2.0% gallium oxide. Also disclosed are articles of manufacture, comprising the shear thinning gel composition, and methods of making article of manufacture having a shear thinning gel composition. Also disclosed are sensors and multiplexed systems utilizing deformable conductors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/947,744 filed Apr. 6, 2018 titled Deformable Conductors and RelatedSensors, Antennas and Multiplexed Systems, which is acontinuation-in-part (CIP) of International Patent ApplicationPCT/US2017/019762 filed Feb. 27, 2017 which is incorporated by referenceand was published on Sep. 8, 2017 as International Publication No. WO2017/151523 A1 which is incorporated by reference and which claimspriority from U.S. Provisional Patent Application Ser. No. 62/301,622filed Feb. 29, 2016 which is incorporated by reference. This applicationalso claims priority from U.S. Provisional Patent Application Ser. No.62/483,307 filed Apr. 7, 2017 which is incorporated by reference. Thisapplication also claims priority from U.S. Provisional PatentApplication Ser. No. 62/483,309 filed Apr. 7, 2017 which is incorporatedby reference.

TECHNICAL FIELD

Embodiments herein relate to liquid wire, and more specifically toliquid wire composed of a gallium indium alloy with integratedmicrostructures, and related sensors and multiplexed systems.

BACKGROUND

There is growing interest in incorporating electronics into everydayobjects, including clothing and textile objects which are expected to bepliable, stretchable and soft. Soft electronics would be able toseamlessly interface with the human body, opening up many newapplications for wearables, medical devices and the prospect ofconformal robotics or ‘soft machines’ which could more safely interactwith humans or delicate items (see, for example, Dickey, ACS Appl MaterInterfaces. 2014 Nov. 12; 6(21): 18369-18379).

Many non-traditional manufacturing methods are being considered tofabricate these soft electronic devices, notably 3D printing. However, amajor stumbling block is the lack of a high conductivity and easilyprocessed stretchable conductor.

Many attempts at stretchable conductors have been tried. One of the mostsuccessful has been microfluidic channels filled with room temperatureliquid metal. Functional devices are created by etching micrometerchannels into polydimethylsiloxane (PDMS), sealing them over and theninjecting metals alloy into the channels to create conductive paths.These alloys can have a melting point as low as −19° C. and so remainfluid under normal conditions. Because the metal conductors are fluid,they can be deformed to an extent limited only by the material creatingthe channels containing them and recover fully. Further, their change inresistance is a purely mechanical function of the wire length and crosssection and so is linear. This affords a major advantage of allowingconductive pathways to also act as sensors.

However, manufacturing devices with these microfluidic channels is verychallenging. PDMS is the preferred substrate, but creating a proper sealaround the channels is expensive, requiring exposure of the channelcontaining layer to oxygen plasma in order to adhere a cap layer toenclose the channel. Once constructed, the channels must be filled via atwo syringe system, where one syringe injects the liquid alloy andanother evacuates the air already present. Failure rates duringconstruction are very high. Anecdotally it's been reported that onlyabout one in twenty fabrication attempts succeeds. Thus, the need existfor other “liquid” metals.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be readily understood by the following detaileddescription in conjunction with the accompanying drawings and theappended claims. Embodiments are illustrated by way of example and notby way of limitation in the figures of the accompanying drawings.

FIGS. 1A-1E are a digital image of a scanning electron microscope (SEM)images showing various gallium containing formulations, in accordancewith various embodiments.

FIGS. 2A-2C are digital images of unsuccessful (A, B) and successful (C)compression tests, in accordance with various embodiments.

FIG. 3 is a digital image Initial observation of high fidelity contacttransfer of metal gel patterns.

FIGS. 4A-4D are digital images of test contact transfer patterns withparticle loaded metal gel. Patterns have trace widths as fine as 0.5 mmand pitches as fine as 0.25 mm, in accordance with various embodiments.

FIG. 5 is a digital image of a patterned pressure sensor, in accordancewith various embodiments.

FIG. 6 is a graph of a strain test of an 8″ trace of Metal Gelencapsulated in silicone, showing the linearity of resistance relativeto degree of strain.

FIG. 7 is an illustration of variable resistors oriented to change dueto strain along either weave or weft orientations.

FIG. 8 is a simple 1×3 grid with 10 variable resistors and a fouranalogue output elements, A, B, C, D. All unique pairings of outputelements create a 6 element vector. By properly weighting the resistanceranges of each variable resistor we can ensure the output vectoruniquely encodes every possible combination of resistances to anarbitrary fidelity.

FIG. 9 is a digital image of a 990 MHz antenna printed from metal gel,in accordance with embodiments disclosed herein.

FIG. 10A is an example trace pattern having a simple line which will actas a variable resistor changing with strain parallel to its path. FIG.10B is an example trace pattern having a return path to allow a signalto be read with i/o ports local to each other, wherein the verticalconnecting bar will provide negligible resistance change for strainmeasured parallel to the main traces. FIG. 10C is an example tracepattern having a zigzag pattern which will multiply theresistance/strain feedback for strain perpendicular to the direction ofthe trace. FIG. 10D is an example trace pattern having a trace with areturn path and resistance/strain feedback multiplier on the horizontalportion, wherein the trace will be sensitive to strain parallel to itsorientation, but not perpendicular.

FIG. 11 is a graph of a measured insertion loss to 6 GHz for of 1.4 mil(35 um) thick Cu reference trace and a 75 um thick metal gel line.Insertion loss rises for both materials from skin effect.

FIG. 12A is a schematic showing encapsulation of a standard parachuteline with multiple cords surrounded by a sheath. FIG. 12B is a schematicshowing Metal gel (1) encased with nylon cords in the sheath creating asingle conductor. FIG. 12C is a schematic showing multiple conductors ina single parachute line wherein individual inner nylon cords may becoated with metal gel and encapsulated in an insulator such as athermoset polyurethane. FIG. 12D is a schematic showing thatalternatively multiple metal gel conductors (3) can be encased inthermoplastic polyurethane and adhered to the outside of the parachuteline sheath.

FIG. 13 is a block diagram of the basic strain sensor using a pair ofmetal gel wires of length L_(s). The two wires have a combinedresistance of R_(s)=R_(s1)+R_(s2)=V_(s)/I_(s), where V_(s) and I_(s) arethe dc voltage and current at the Wheatstone bridge sense port. TheWheatstone bridge has an output V_(o), which is proportional to R_(s),which is fed into an ADC to create a digital strain data output.

FIG. 14 is a block diagram showing how a diplexer allows the DC current,I_(s), to flow through the strain sensor loop via L_(d), while the RFsignal is coupled by C_(d) into the loop and removed by C₁ and C₂. Theinductor L_(d) also prevents the RF signal from being short circuited.

FIG. 15A illustrates a method of creating controlled impedancetransmission lines using metal gel having a coaxial interconnect with ametal gel center (1) conductor (that could even be a coated nylon cord)surrounded by an insulating encapsulation layer and a metal gel outerlayer (2) with a final outer encapsulation layer to stabilize thestructure; this design has an outer conductor of metal gel (2) appliedaround the insulated center conductor (1) to create a coaxialtransmission line having an impedance of the range of 30 to 100 ohms.FIG. 15B illustrates a method of creating controlled impedancetransmission lines using metal gel having two metal gel lines in a “twinlead” (also called “bifilar”) arrangement. FIG. 15C illustrates a methodof creating controlled impedance transmission lines using metal gelhaving an outer metal gel layer applied to the structure in FIG. 15B toallow lower impedances, which also reduces radiation and shields the twolines from electromagnetic interference (EMI).

FIG. 16 is a cross-sectional view illustrating an embodiment of a devicefor capacitively sensing shear according to the inventive principles ofthis patent disclosure.

FIG. 17 is a cross-sectional view illustrating an embodiment of a devicefor sensing deformation using changes in characteristic impedanceaccording to the inventive principles of this patent disclosure.

FIG. 18 is a plan view illustrating an embodiment of a device forcapacitively sensing compression at various points of an array accordingto the inventive principles of this patent disclosure.

FIG. 19 is a plan view illustrating an embodiment of a device forinductive sensing according to the inventive principles of this patentdisclosure.

FIG. 20 illustrates an embodiment of a strain controlled oscillator thatuses deformable conductors that function as both a strain sensor andtransmission line according to some inventive principles of this patentdisclosure.

FIG. 21 is a cross-sectional view of a transmission line structuresuitable for use with deformable conductors according to some inventiveprinciples of this patent disclosure.

FIG. 22 is a plan view illustrating an embodiment of a diplexed strainsensor using a slot line structure according to some inventiveprinciples of this patent disclosure.

FIG. 23 is a cross-sectional view of another transmission line structuresuitable for use with deformable conductors according to some inventiveprinciples of this patent disclosure.

FIG. 24 is a plan view illustrating another embodiment of a diplexedstrain sensor using a coplanar waveguide structure according to someinventive principles of this patent disclosure.

FIG. 25 illustrates the return loss versus stretch for a bow tie antennafabricated with metal gel according to the inventive principles of thispatent disclosure.

FIG. 26 illustrates a bow tie antenna structure according to someinventive principles of this patent disclosure.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which are shown byway of illustration embodiments that may be practiced. It is to beunderstood that other embodiments may be utilized and structural orlogical changes may be made without departing from the spirit or scopeof the present disclosure. Therefore, the following detailed descriptionis not to be taken in a limiting sense, and the scope of embodiments isdefined by the appended claims and their equivalents.

Unless otherwise explained, all technical and scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the disclosed subject matter belongs.Definitions of common terms in chemistry terms may be found in TheMcGraw-Hill Dictionary of Chemical Terms, 1985, and The CondensedChemical Dictionary, 1981. Except as otherwise noted, the methods andtechniques of the present disclosure are generally performed accordingto conventional methods well known in the art and as described invarious general and more specific references that are cited anddiscussed throughout the present specification. See, e.g., Loudon,Organic Chemistry, Fourth Edition, New York: Oxford University Press,2002, pp. 360-361, 1084-1085; Smith and March, March's Advanced OrganicChemistry: Reactions, Mechanisms, and Structure, Fifth Edition,Wiley-Interscience, 2001; or Vogel, A Textbook of Practical OrganicChemistry, Including Qualitative Organic Analysis, Fourth Edition, NewYork: Longman, 1978.

Various operations may be described as multiple discrete operations inturn, in a manner that may be helpful in understanding embodiments;however, the order of description should not be construed to imply thatthese operations are order dependent.

The description may use perspective-based descriptions such as up/down,back/front, and top/bottom. Such descriptions are merely used tofacilitate the discussion and are not intended to restrict theapplication of disclosed embodiments.

The terms “coupled” and “connected,” along with their derivatives, maybe used. It should be understood that these terms are not intended assynonyms for each other. Rather, in particular embodiments, “connected”may be used to indicate that two or more elements are in direct physicalwith each other. “Coupled” may mean that two or more elements are indirect physical contact. However, “coupled” may also mean that two ormore elements are not in direct contact with each other, but yet stillcooperate or interact with each other.

As used herein, the singular terms “a,” “an,” and “the” include pluralreferents unless context clearly indicates otherwise. Similarly, theword “or” is intended to include “and” unless the context clearlyindicates otherwise. Also, as used herein, the term “comprises” means“includes.” Hence “comprising A or B” means including A, B, or A and B.

Except as otherwise noted, any quantitative values are approximatewhether the word “about” or “approximately” or the like are stated ornot. The materials, methods, and examples described herein areillustrative only and not intended to be limiting. Any molecular weightor molecular mass values are approximate and are provided only fordescription.

The description may use the terms “embodiment” or “embodiments,” whichmay each refer to one or more of the same or different embodiments.Furthermore, the terms “comprising,” “including,” “having,” and thelike, as used with respect to embodiments, are synonymous.

A. Introduction

Flexible conductors are needed for numerous applications in electronics.Wearable devices, conforming sensors, flexible displays, soft roboticactuators and stretchable interconnects all require an electricallyconductive medium able to both repeatably bend and stretch. Ideally aflexible conductor should provide no material resistance to the motionof a substrate it is adhered to while maintaining conduction throughmany cycles of stretching and flexing. A liquid conductor is ideallysuited for this task.

As briefly touched on above, “liquid” metal conductors use eutecticalloys of gallium, usually mixed with indium and tin, which are embeddedwithin microfluidic channels. Typically these alloys include:gallium-indium (usually 75% gallium, 25% indium) and gallium-indium-tin(most commonly 68.5% gallium, 21.5% indium, 10% tin). The gallium alloyfluids have low viscosities and high surface tensions. While thesealloys may be good conductors, they have significant drawbacks that havehampered their widespread adoption. For example, the alloys themselvesare difficult to process. In addition, the microfluidic channels areprone to leaking or failing irreversibly if the substrate the alloy isembedded in fatigues. Lastly, the alloys form an oxide layer on exposureto atmosphere, which is not conductive and can lead to failures atjunctions between flexible wires and hard components. Thus, it would bean important advance to the art to provide a fluid that is easy toprocess, protected against oxidization, and has self-healing propertiesto allow functioning even as its substrate begins to wear. The currentdisclosure fulfills those needs.

Disclosed herein is a novel composite material discovered by theinventor that is composed of a gallium alloy and gallium oxidecomposition that includes distributed microstructures formed from thegallium oxide within the bulk gallium alloy. In embodiments themicrostructures are formed from sheets of gallium-oxide that form on thesurface of the bulk gallium to induce the distributed microstructurewhen mixed into the gallium alloy. The alloy is bound into a crosslinked nanostructure of oxide ribbons, which serve a purpose similar topolymer gelling agents in common water based gels. The gel is stabilizedusing sub-micron scale particles to make a high viscosity, easilywettable and leak resistant Bingham Plastic (a fluid which evidences theproperties of a solid until a shear force is applied) which can beconsistently patterned onto most surfaces at room temperature. Oncepatterned the result is a high conductivity fluid interconnect whichdoes not affect the material properties of its substrate. This gel isfluid at room temperature and has a freezing point at −5 centigrade. Theend material has conductivities on the scale of 2-8*10⁵ S/m, dependingon the degree of stabilization needed, and since it is relatively easyto pattern conductors up to 100 um thick the resulting sheet resistanceis quite low compared to other flexible conductors. The disclosedcomposition generally forms a paste like material. The gallium oxide, inconjunction with a gallium alloy fluid, form micro and nano-structures.These structures can bear a small amount of force, depending on theirgeometry. By distributing a very large number of irregularly shapedmicro and nano-structures composed of gallium oxide through the bulk ofa gallium alloy fluid a new and novel composite fluid can be created,with high viscosity and non-Newtonian rheological properties. The fluidbehaves similarly to a Bingham Plastic, holding structure until a stressis applied. As disclosed herein the creation and distribution of thesemicro and nano-structures can be achieved by multiple methods. In oneembodiment, the creation and distribution of gallium oxide micro andnano-structures is achieved by coating nano-particles and/ormicro-particles in gallium-indium-tin enveloped in gallium oxide, andsuspending them in a fluid of gallium-indium-tin through application ofshear by means of shaking or mixing.

B. Overview of Several Embodiments

Aspects of the present disclosure relate to an electrically conductivecompositions, for example with a paste like consistency, created bytaking advantage of the structure provided by gallium oxide mixed into aeutectic gallium alloy in such a way as to provide micro ornano-structures capable of altering the bulk material properties of theeutectic gallium alloy. In some embodiments, the an electricallyconductive compositions can be characterized as a conducting shearthinning gel composition, or a material having the properties of aBingham plastic. In embodiments, a disclosed composition has a viscosityranging from about 10,000,000 centipoise to about 40,000,000 centipoiseunder low shear and about 150 to 180 at high shear. For example undercondition of low shear the composition has a viscosity of about10,000,000 centipoise, about 15,000,000 centipoise, about 20,000,000centipoise, about 25,000,000 centipoise, about 30,000,000 centipoise,about 45,000,000 centipoise, or about 40,000,000 centipoise underconditions of low shear. Under condition of high shear the compositionhas a viscosity of about 150 centipoise, about 155 centipoise, about 160centipoise, 165 centipoise, about 170 centipoise, about 175 centipoise,or about 180 centipoise.

In embodiments, a disclosed composition includes a mixture of a eutecticgallium alloy and gallium oxide, wherein the mixture of eutectic galliumalloy and gallium oxide has a weight percentage (wt %) of between about59.9% and about 99.9% eutectic gallium alloy, such as between about 67%and about 90%, and a wt % of between about 0.1% and about 2.0% galliumoxide such as between about 0.2 and about 1%. For example, a disclosedcomposition can have about 60%, about 61%, about 62%, about 63%, about64%, about 65%, about 66%, about 67%, about 68%, about 69%, about 70%,about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%,about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%,about 97%, about 98%, about 99%, or greater, such as about 99.9%eutectic gallium alloy, and about 0.1%, about 0.2%, about 0.3%, about0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about1.0%, about 1.1%, about 1.2%, about 1.3%, about 1.4%, about 1.5%, about1.6%, about 1.7%, about 1.8%, about 1.9%, and about 2.0% gallium oxide.

In embodiments, the eutectic gallium alloy can include gallium-indium orgallium-indium-tin in any ratio of elements. In certain embodiments, aeutectic gallium alloy includes gallium and indium. In certainembodiments a disclosed composition has percentage of gallium by weightin the gallium-indium alloy that is between about 40% and about 95%,such as about 40%, about 41%, about 42%, about 43%, about 44%, about45%, about 46%, about 47%, about 48%, about 49%, about 50%, about 51%,about 52%, about 53%, about 54%, about 55%, about 56%, about 57%, about58%, about 59%, about 60%, about 61%, about 62%, about 63%, about 64%,about 65%, about 66%, about 67%, about 68%, about 69%, about 70%, about71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%,about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%,about 91%, about 92%, about 93%, about 94%, or about 95%.

In certain embodiments a disclosed composition has percentage of indiumby weight in the gallium-indium alloy that is between about 5% and about60%, such as about 5%, about 6%, about 7%, about 8%, about 9%, about10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%,about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29%,about 30%, about 31%, about 32%, about 33%, about 34%, about 35%, about36%, about 37%, about 38%, about 39%, about 40%, about 41%, about 42%,about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about49%, about 50%, about 51%, about 52%, about 53%, about 54%, about 55%,about 56%, about 57%, about 58%, about 59%, or about 60%.

In certain embodiments, a eutectic gallium alloy includes gallium andtin. In certain embodiments a disclosed composition has percentage oftin by weight in the alloy that is between about 0.001% and about 50%,such as about 0.001%, about 0.005%, about 0.01%, about 0.05%, about0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about0.7%, about 0.8%, about 0.9%, about 1%, about 1.5%, about 2%, about 3%,about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%,about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%,about 24%, about 25%, about 26%, about 27%, about 28%, about 29%, about30%, about 31%, about 32%, about 33%, about 34%, about 35%, about 36%,about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%,or about 50%.

In embodiments, one or more micro-particles or sub-micron scaleparticles are blended with the gallium alloy and gallium oxide. Inembodiments, the particles are suspended, either coated in eutecticgallium alloy or gallium and encapsulated in gallium oxide or not coatedin the previous manner, within eutectic gallium alloy fluid. Theseparticles can range in size from nanometer to micrometer and can besuspended in gallium, gallium-indium alloy, or gallium-indium-tin alloy.Particle to alloy ratio can vary, in order to change fluid properties.In embodiments the micro and nano-structures are blended within themixture through sonication or other mechanical means. In embodiments, adisclosed composition includes a colloidal suspension of micro andnano-structures within the gallium alloy/gallium oxide mixture.

In embodiments, as disclosed composition further includes one or moremicro-particles or sub-micron scale particles dispersed within themixture. This can be achieved by suspending particles, either coated ineutectic gallium alloy or gallium and encapsulated in gallium oxide ornot coated in the previous manner, within eutectic gallium alloy fluid.These particles can range in size from nanometer to micrometer and canbe suspended in gallium, gallium-indium alloy, or gallium-indium-tinalloy. Particle to alloy ratio can vary, in order to change fluidproperties. In addition, the addition of any ancillary material tocolloidal suspension or gallium alloy paste in order to enhance ormodify its physical, electrical or thermal properties. The distributionof micro and nano-structures within eutectic gallium alloy can beachieved through sonication or other mechanical means without theaddition of particles. In certain embodiments, the one or moremicro-particles or sub-micron particles are blended with the mixturewith wt % of between about 0.001% and about 40.0% of micro-particles,for example about 0.001%, about 0.005%, about 0.01%, about 0.05%, about0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about0.7%, about 0.8%, about 0.9%, about 1%, about 1.5%, about 2%, about 3%,about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%,about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%,about 24%, about 25%, about 26%, about 27%, about 28%, about 29%, about30%, about 31%, about 32%, about 33%, about 34%, about 35%, about 36%,about 37%, about 38%, about 39%, or about 40.

In embodiments, the particles can be soda glass, silica, borosilicateglass, quartz, oxidized copper, silver coated copper, non-oxidizedcopper, tungsten, super saturated tin granules, glass, graphite, silvercoated copper, such as silver coated copper spheres, and silver coatedcopper flakes, copper flakes, or copper spheres, or a combinationthereof, or any other material that can be wetted by gallium. In someembodiments, the one or more micro-particles or sub-micron scaleparticles are in the shape of spheroids, rods, tubes, a flakes, plates,cubes, prismatic, pyramidal, cages, and dendrimers. In certainembodiments, the one or more micro-particles or sub-micron scaleparticles are in the size range of about 0.5 microns to about 60microns, as about 0.5 microns, about 0.6 microns, about 0.7 microns,about 0.8 microns, about 0.9 microns, about 1 microns, about 1.5microns, about 2 microns, about 3 microns, about 4 microns, about 5microns, about 6 microns, about 7 microns, about 8 microns, about 9microns, about 10 microns, about 11 microns, about 12 microns, about 13microns, about 14 microns, about 15 microns, about 16 microns, about 17microns, about 18 microns, about 19 microns, about 20 microns, about 21microns, about 22 microns, about 23 microns, about 24 microns, about 25microns, about 26 microns, about 27 microns, about 28 microns, about 29microns, about 30 microns, about 31 microns, about 32 microns, about 33microns, about 34 microns, about 35 microns, about 36 microns, about 37microns, about 38 microns, about 39 microns, about 40 microns, about 41microns, about 42 microns, about 43 microns, about 44 microns, about 45microns, about 46 microns, about 47 microns, about 48 microns, about 49microns, about 50 microns, about 51 microns, about 52 microns, about 53microns, about 54 microns, about 55 microns, about 56 microns, about 57microns, about 58 microns, about 59 microns, or about 60 microns.

Aspects of this disclosure further relate to methods of making aconducting shear thinning gel composition. In embodiments, the methodsinclude blending surface oxides formed on a surface of a gallium alloyfluid into the bulk of the gallium alloy fluid by shear mixing of thesurface oxide/alloy interface; and inducing a cross linkedmicrostructure in the surface oxides; thereby forming a conducting shearthinning gel composition. In embodiments, a colloidal suspension ofmicro-structures is formed within the gallium alloy/gallium oxidemixture, for example as, gallium oxide particles and/or sheets.

In embodiments, the surface oxides are blended at a ratio of betweenabout 59.9% (by weight) and about 99.9% eutectic gallium alloy, to about0.1% (by weight) and about 2.0% gallium oxide. For example percentage byweight of gallium alloy blended with gallium oxide is about 60%, 61%,about 62%, about 63%, about 64%, about 65%, about 66%, about 67%, about68%, about 69%, about 70%, about 71%, about 72%, about 73%, about 74%,about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%,about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about94%, about 95%, about 96%, about 97%, about 98%, about 99%, or greater,such as about 99.9% eutectic gallium alloy while the weight percentageof gallium oxide is about 0.1%, about 0.2%, about 0.3%, about 0.4%,about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1.0%,about 1.1%, about 1.2%, about 1.3%, about 1.4%, about 1.5%, about 1.6%,about 1.7%, about 1.8%, about 1.9%, and about 2.0% gallium oxide. Inembodiments, the eutectic gallium alloy can include gallium-indium orgallium-indium-tin in any ratio of elements. In certain embodiments, aeutectic gallium alloy includes gallium and indium. In certainembodiments the weight percentage of gallium in the gallium-indium alloyis between about 40% and about 95%, such as about 40%, about 41%, about42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%,about 49%, about 50%, about 51%, about 52%, about 53%, about 54%, about55%, about 56%, about 57%, about 58%, about 59%, about 60%, about 61%,about 62%, about 63%, about 64%, about 65%, about 66%, about 67%, about68%, about 69%, about 70%, about 71%, about 72%, about 73%, about 74%,about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%,about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about94%, or about 95%. In certain embodiments the weight percentage ofindium in the gallium-indium alloy is between about 5% and about 60%,such as about 5%, about 6%, about 7%, about 8%, about 9%, about 10%,about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%,about 24%, about 25%, about 26%, about 27%, about 28%, about 29%, about30%, about 31%, about 32%, about 33%, about 34%, about 35%, about 36%,about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%,about 50%, about 51%, about 52%, about 53%, about 54%, about 55%, about56%, about 57%, about 58%, about 59%, or about 60%. In certainembodiments, a eutectic gallium alloy includes gallium, indium, and tin.In certain embodiments the weight percentage of tin in thegallium-indium-tin alloy is between about 0.001% and about 50%, such asabout 0.001%, about 0.005%, about 0.01%, about 0.05%, about 0.1%, about0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about0.8%, about 0.9%, about 1%, about 1.5%, about 2%, about 3%, about 4%,about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%,about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%,about 25%, about 26%, about 27%, about 28%, about 29%, about 30%, about31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%,about 38%, about 39%, about 40%, about 41%, about 42%, about 43%, about44%, about 45%, about 46%, about 47%, about 48%, about 49%, or about50%.

In embodiments, one or more micro-particles or sub-micron scaleparticles are blended with the gallium alloy and gallium oxide. Incertain embodiments, the one or more micro-particles or sub-micronparticles are blended with the mixture with wt % of between about 0.001%and about 40.0% of micro-particles in the composition, for example about0.001%, about 0.005%, about 0.01%, about 0.05%, about 0.1%, about 0.2%,about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%,about 0.9%, about 1%, about 1.5%, about 2%, about 3%, about 4%, about5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%,about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about25%, about 26%, about 27%, about 28%, about 29%, about 30%, about 31%,about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about38%, about 39%, or about 40. In embodiments the particles can be sodaglass, silica, borosilicate glass, quartz, oxidized copper, silvercoated copper, non-oxidized copper, tungsten, super saturated tingranules, glass, graphite, silver coated copper, such as silver coatedcopper spheres, and silver coated copper flakes, copper flakes or copperspheres or a combination thereof, or any other material that can bewetted by gallium. In some embodiments the one or more micro-particlesor sub-micron scale particles are in the shape of spheroids, rods,tubes, a flakes, plates, cubes, prismatic, pyramidal, cages, anddendrimers. In certain embodiments, the one or more micro-particles orsub-micron scale particles are in the size range of about 0.5 microns toabout 60 microns, as about 0.5 microns, about 0.6 microns, about 0.7microns, about 0.8 microns, about 0.9 microns, about 1 microns, about1.5 microns, about 2 microns, about 3 microns, about 4 microns, about 5microns, about 6 microns, about 7 microns, about 8 microns, about 9microns, about 10 microns, about 11 microns, about 12 microns, about 13microns, about 14 microns, about 15 microns, about 16 microns, about 17microns, about 18 microns, about 19 microns, about 20 microns, about 21microns, about 22 microns, about 23 microns, about 24 microns, about 25microns, about 26 microns, about 27 microns, about 28 microns, about 29microns, about 30 microns, about 31 microns, about 32 microns, about 33microns, about 34 microns, about 35 microns, about 36 microns, about 37microns, about 38 microns, about 39 microns, about 40 microns, about 41microns, about 42 microns, about 43 microns, about 44 microns, about 45microns, about 46 microns, about 47 microns, about 48 microns, about 49microns, about 50 microns, about 51 microns, about 52 microns, about 53microns, about 54 microns, about 55 microns, about 56 microns, about 57microns, about 58 microns, about 59 microns, or about 60 microns.

Aspect of the present disclosure related to articles of manufacture thatincludes a disclosed composition as well as methods of making suchcompositions. There is growing interest in incorporating electronicsinto everyday objects, including clothing and textile objects which areexpected to be pliable, stretchable and soft. Soft electronics would beable to seamlessly interface with the human body, opening up many newapplications for wearables, medical devices and the prospect ofconformal robotics or ‘soft machines’ which could more safely interactwith humans or delicate items.

In certain embodiments the article of manufacture comprises anelectronic device. In certain embodiments the article of manufacturecomprises a fabric, a plastic film and/or a membrane. In certainembodiments the disclosed compositions are integrated in sensors, forexample sensors for us in detection strain and/or shear sensing. By wayof example deforming liquid wire composed of a disclosed composition cancreate measurable changes in resistance, capacitance, inductance,impedance or characteristic frequency depending on the conductorgeometry. For example the compositions can be used as sensors to detectstrain and/or shear on any substrate. For example, a composition can beintegrated into a ‘geotextile’ for use in reinforcing a berm or levy. Inone such example, a long plastic encased wire made of a disclosedcomposition could detect slumping in the earthwork structure, giving anearly warning of collapse. In another example a disclosed compositioncould be patterned onto parachute suspension lines to give real timestrain feedback that could be used to control an automated steerableparachute.

In certain embodiments the article of manufacture comprises an articleof bodywear comprising a base fabric; and one or more elements of thedisclosed composition disposed thereon. In various embodiments, a basefabric, for example for body gear, is disclosed that may use one or moreelements of the disclosed composition disposed thereon coupled to thesurface of the base fabric, such as the outward or inward facing surfaceof a fabric. In an embodiment, the disclosed composition conductselectric current between various other elements of the garment, forexample a power source, such as a battery and other integratedelectronic devices, such as sensors.

In some embodiments, article of bodywear may include components forcollecting information and/or processing the collected information,coupled to a disclosed composition. For example article of bodywear mayinclude components monitoring one or more physical conditions of thewearer, such a body vital signs, for example as heart rate or EKG, pulseand temperature, and movement. In certain embodiments a disclosedcomposition is configured as a pressure sensor.

Generally, a sufficient surface area of the base fabric should beexposed to provide the desired base fabric function (e.g., stretch,drape, texture, breathability, moisture vapor transfer, airpermeability, and/or wicking). For example, if there is too littleexposed base fabric, properties such as moisture vapor transfer and/orair permeability may suffer, and even disproportionately to thepercentage of coverage.

In embodiments, the electrically conductive compositions are in therange from about 0.1 mm in width to about 10.0 mm in width, such asabout 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0,6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, or 10.0 mm (sometime greater) inwidth or any value or range within.

In certain embodiments, the amount electrically conductive compositionand/or placement is selected to contain costs and create a material thatis aesthetically pleasing. In embodiments, the electrically conductivecompositions, has a thickness in the range from about 0.05, mm to about5 mm thick, such as about 0.05, about 0.1, about 0.5, about 1.0, about1.5, about 2.0, about 2.5, about 3.0, about 3.5, about 4.0, about 4.5,about 5.0, mm thick, or any value or range within, although lesser andgreater thicknesses are also contemplated.

In accordance with various embodiments, the base fabric may be a part ofany form of body gear, such as bodywear, blankets, tents, rain flys,umbrellas, or sun shade, or any material or apparatus. Bodywear, as usedherein, includes anything worn on the body, such as, but not limited to,athletic wear such as compression garments, t-shirts, shorts, tights,sleeves, headbands and the like, outerwear, such as jackets, pants,leggings, shirts, hats, and the like, and footwear.

In various embodiments, the amount electrically conductive compositionand/or placement may be disposed on a base fabric having one or moredesired properties or characteristics. For example, the base fabric mayhave properties such as air permeability, moisture vapor transfer,and/or wickability, which are common needs for bodywear used in bothindoor and outdoor applications. In some embodiments, the base fabricmay have other desirable attributes, such as abrasion resistance,anti-static properties, anti-microbial activity, water repellence, flamerepellence, hydrophilicity, hydrophobicity, wind resistance, solarprotection, SPF protection, resiliency, stain resistance, wrinkleresistance, and the like. In other embodiments, separations between theamount electrically conductive compositions may help allow the basefabric to have a desired drape, look, and/or texture. Suitable basefabrics may include nylon, polyester, rayon, cotton, spandex, wool,silk, or a blend thereof, or any other material having a desired look,feel, weight, thickness, weave, texture, or other desired property.

In various embodiments, single-layer of base fabric may be usedcomprising the base fabric, whereas other embodiments may use multiplelayers of fabric, including a layer of the base fabric, coupled to oneor more other layers.

In various embodiments, the placement, pattern the amount electricallyconductive composition may vary. In various embodiments, the pattern ofthe amount electrically conductive composition and/or placement may besymmetrical, ordered, random, and/or asymmetrical.

Aspects of this disclosure further relate to methods of making anarticle of manufacture having a shear thinning gel composition asdisclosed above. In such methods, the shear thinning gel composition isprinted onto at least one surface of the article of manufacture.

In certain embodiments, a disclosed composition is printed or otherwisetransferred to substrate. In some embodiments, printing comprises screenprinting. In some examples printing is done by contact transfer, forexample using 3D printing stamp molds cast is silicone rubber and/orpolyurethane rubber stamps. A parameter in transfer contacts is thesurface energy of the material to be transferred, the contact pad andthe substrate. A fluid will generally wet to a surface with higherenergy than its own surface energy and preferentially wet to a substratewith a yet higher energy. Silicone rubbers (PDMS) have unusually lowsurface energies and are often used as the transfer agent in contacttransfer printing. In other embodiments, a disclosed composition istransferred to a substrate using a saturated sponge is pressed through amask to transfer material. A number of polyurethane and PDMS foams areavailable which are for the sponge methods.

The subject matter of the present disclosure is further illustrated bythe following non-limiting Examples.

EXAMPLE Example 1 Method of Material Formation

Initially working with a commercially available gallium-indium-tin(68.5, 21.5, 10) alloy (Galistan), it was observed that gallium basedalloys form oxide layers very quickly in atmosphere. During the processof injecting the liquid metal into PDMS microfluidic channels,Hydrochloric Acid (HCL) was being used to reduce oxide layers on samplesto reduce waste and allow ‘clean’ non-oxidized devices to be built. Inthe course of this process it was observed that sample exhibited strangephysical behavior when being reduced by HCL. For example it did not formregular Galinstan, but rather made a viscous material. The material washarvestable in small quantities from my commercially obtained Galistansamples.

An initial attempt was made to synthesize a material similar to foamfrom Galinstan by blending in 30 micron glass beads. In the presence ofoxygen galinstan wetted readily to glass via its oxide layer. It wasinitially hoped that it would ‘wet’ to glass beads in this manner and aslurry of Galinstan and glass would be formed in this way, which mightbe high viscosity and easily formed into arbitrary shapes.

It had previously been reported that the only mechanism by whichgallium-indium and related alloys wets to any non-metallic surface isthrough the adhesion of its oxide layer and the resultant trapping ofthe fluid under that layer. It was the hypothesis thatgallium-indium-tin would wet in such a manner to the beads, with a thinlayer of fluid metal directly in contact with the glass, trapped inplace by an oxide layer. Through mixing the glass beads would comerepeatedly in contact with atmosphere, forming successive layers ofoxide trapping successive layers of gallium-indium-tin. When thesestructures were resubmerged, shear forces from the mixing were expectedto cause the oxide layers to break and form dispersed structure,allowing a colloidal suspension of the glass beads and upping theviscosity of the fluid.

This method worked well with 30 micron beads and a variety of othersizes. This led to the discovery that any fine network of interlinkedgallium-oxide structure would absorb gallium-indium alloy and wouldprovide an internal structure to the fluid which would increaseviscosity. With a higher viscosity the fluid would be more easilyextrudable and could be reliably formed into conducting geometries usingtraditional printing techniques such as nozzle deposition or stenciledprinting. The resulting high viscosity fluid is referred to variously asGallium-Indium Gel, Gallium-Indium alloy Gel, Metal Gel or simply Gel.

Example 2 Addition Method of Material Formation

First, microstructures of gallium oxide were created by sonicatinggallium-indium-tin which was wetted onto a plane of glass. Thesonication caused microstructures to form on the gallium-oxide surface.Successive sonication and mixing sessions blended these structures intothe bulk of the fluid, eventually resulting in a gel consisting ofgallium-indium-tin and approximately 0.84% oxide. This gel was lessprone to separation than that made with glass beads and has a naturallymuch higher bulk conductivity. Interestingly, hydrochloric acid, oftenused to reduce the oxide on gallium alloys, reduces only the surfaceoxide on gel produced in this manner, leaving the internal structureintact. This contrast with gel made with glass beads, which is fullyreduced by HCL, causing a complete separation of the beads from the geland a lowering of viscosity.

Example 3 Addition Method of Material Formation

A third successful technique involved using a mixing bar partiallysubmerged in a bath of gallium-indium or gallium-indium-tin and rotatingat very high RPM in order to create a vortex. A vortex created in such away causes thin unstable walls of gallium-indium and its oxide layer toform around the mixing bar, extending multiple centimeters above thefluid level. Due to these walls the vortex has a high surface area andsublimates a large amount of oxide into the fluid. The fluid quicklyincreases in viscosity, necessitating orbital mixing. The resultingfluid is not homogenous, gallium-indium Gel floats on the surface, dueto blended in air bubbles, while low viscosity gallium-indium alloyforms a pool on the bottom. The Gel can be drained by placing it on anincline, then gathered and vacuum cycled to pull out the air. Theresulting gel is comparable to that produced through sonication.

Example 4 Creation of Stamp Transferable Compositions

Both Gallium and Indium are expensive. Their conductivity is adequate,but much lower than copper or silver (3.46×106 S/m compared to 58.5×106S/m for copper). It was thought to be desirable to create a suspensionof additives in the gel both to decrease cost and increase conductivity.Multiple additives were attempted.

Both microsphere and flake gels are resistant to displacement whenpressure is applied during encapsulation by adhesives or thermoplasticwelding.

An innovation was that both flake and pure copper loaded gels becomestamp transferable. A regular letter press stamp can be coated with thegel+additive material and then pressed against a suitable substrate, andthe pattern on the stamp will be transferred with high fidelity.Features as small as 0.5 mm were created in this manner, with pitches assmall as 0.25 mm. Such depositions were extremely thin, about 25micometers.

Example 5 Creation of Stamp Transferable Compositions

Macro contact printing has been tried, up to now without success forother gallium containing liquids. For stamp lithography, attempts totransfer a solid line and filled rectangle onto an elastomer substrateusing both flat stamps and textured stamps have also been tried withoutsuccess. Although this transfer method is similar to existing approachesin the past other groups were not successful in extending this techniqueto liquid-phase Galn alloy. For example Galinstan does not wet theelastomer in some regions and coalesces into droplets in others. In thecase of the textured stamp, droplets deposited by each dimple do notcoalesce uniformly. This uneven wetting may result from non-uniformwetting during “inking”, when the stamp is initially coated withGalinstan, or from non-uniform contact pressures during transfer.

These problems were overcome with the disclosed compositions by mixinglow micron and nanoscale particles into the gallium alloy/oxide gel.While not being bound by theory, it is believed the added particlesstick to the oxide structures and do not float free in the galliummetal. The reinforce the oxide, ensures it breaks in larger chunks andgenerally constrains flow in the system. Perhaps more importantly, whena rupture does occur the flow of metal likely picks up the addedparticles+oxide and carries it along, which impedes the free flow. Thereis also likely an interaction between gallium, indium or tin and thesilver or copper in some of the metallic particles used which may formunstable intermetallics, which create further fine structure in thefluid, impeding its free flow.

Several loading schemes were tried for each additive. All weremechanically mixed at a steady addition rate into pre-prepared gel.Loading as high as 54% was attempted, though higher loadings of metalcauses hardening of the resulting mixture through an unknown process(likely formation of alloys or intermetallics).

It was found that loadings of silver coated copper flake between 10-30%by weight created a composite material with a consistency similar toclay that spread into very uniform flat sheets when deposited with aspatula or brush. Scanning electron microscope (SEM) images showedsheets of deposited material to be uniform in height to a remarkablethough not yet precisely measured degree (See FIGS. 1A-1E). FIG. 1Ashows regular unprocessed gallium-indium-tin (note it is blurry becauseit has a very low viscosity and so is vibrating due to the electron beamimpacting. FIG. 1B shows a micron scale flake stabilized gel (image 500microns across), FIG. 1C shows unstabilized gel (90 microns across),FIG. 1D shows unstabalized gel whipped into a standing shape, to showits semi-solid properties (75 microns across), FIG. 1E unstabalized gel(250 microns view).

Once encapsulated, sheets appear fluid and will stretch and reform underthe forces of their encapsulating channel. Copper microspheres orflakes, loaded at 10-30% weight creates a more viscous fluid, becomingsomewhat solid and crumbly near the upper range of loading.

To test compressibility new formulations were pressed between layers of‘rescue tape’ a self adhering PDMS substrate available commercially, andthey were checked the uniformity of the flow due to compression.

FIGS. 2A and B show unsuccessful (A, B) and successful (C compressiontests side by side. Note the ‘sprues’ jetting off the main body of theunsuccessful compressions. These are caused by unrestrained flow ofgallium metal which is moving separately from the composite system. Incontrast, the particle additive loading in the successful test is suchthat the system must flow together and spreads evenly on compression.This is very desirable for encapsulating the conducting gel usingestablished industrial techniques such as thermowelding plastic filmsaround a deposited pattern. In the course of carrying out thesecompression tests it was observed that patterns were transferred betweenthe substrates with very high fidelity when peeled apart (see FIG. 3)

To further test the promising contact printing techniques a ‘celticknot’ pattern art stamp was used that had a variety of trace widths,pitches and patterns. FIGS. 4A-4D show the initial trials with thatstamp produced excellent results. Patterns with trace widths as fine as0.5 mm and pitches as fine as 0.25 mm.

The transfer process was highly dependent on how much metal gel isloaded onto the stamp initially, how even the substrate and stamp areand how much pressure is applied

With these techniques, useful devices can be made with stamptransferring. FIG. 5 shows an encapsulated stamp, with leads attached.This configuration acts as a pressure sensor. When pressure is appliedthe pattern deflects and compresses, changing its resistance measurably.With a higher fidelity transfer printing process and customized tracepatterns this could be a very cheap and very useful pressure sensor.Total build time was approximately 1 minute by hand, including leadattachment and potting. This manufacture process is very scalable andallows the quick patterning of arbitrary trace geometries in twodimensions.

Example 6 Strain Sensing with Eutectic Metal Gels

The disclosed formulations enable large scale strain and deformationsensing through use of eutectic metal gel composite materials that canbe printed in a manner similar to an ink or paint onto a variety ofsubstrates in order to create conductive traces. Because the disclosedmaterial are an amorphous room temperature fluid, they can be deformedand stretched without fatiguing. A thin trace laid down on a plasticfabric liner can flex and stretch without affecting the feel of thefabric. Encapsulating such a trace with a second layer of fabric linerwill create a sealed conductive pathway. These applications have alreadybeen demonstrated for use in strain sensors and for non-sensing lowprofile and stretchable wires for smart sports clothing.

The amorphous metal structure of the disclosed materials provides thatwhen stretched or otherwise deformed there is linear resistance changewhich can be used for sensing (see FIG. 6). When patterned onto aparachute canopy and integrated with a Wheatstone bridge and an Analogto Digital Converter, resistance changes can be used to measure dynamicforces and strains during parachute deployment.

Any segment of metal gel wire will serve as a variable conductor thevariance of which will be a function of strain parallel to theconductor. This allows a large number of strain sensing patterns to bebuilt, with various resolutions. In the simplest case two traces couldbe patterned onto each gore on a parachute, one traveling in the weftdirection and one traveling in the weave direction (see FIG. 7). Bymeasuring conduction changes on both, a strain profile for theindividual parachute gore can be drawn. With correct patterning certainportions of traces can have a disproportionately high linear resistancechange in response to strain. A zigzag pattern for example will showdisproportionately high resistance change if strained in an axisperpendicular to the path of the trace. Using this feature, multipletraces could be built along a gore with appropriate patterning over anarea of interest for gaining strain information. This would increase theresolution of strain sensing over the gore and allow a complete strainmap to be extrapolated.

A very high resolution could be achieved by building a mesh ofinterconnecting metal gel traces. Each segment of the mesh would be avariable resistor dependent on strain in either the weft or weavedirection depending on its orientation. All unique pairings of outputelements create a 6 element vector. By properly weighting the resistanceranges of each variable resistor it can be ensured that the outputvector uniquely encodes every possible combination of resistances to anarbitrary fidelity (see, for example FIG. 8).

Solving for resistance values in a connected mesh of variable resistorsbased on a finite i/o vector is a well understood problem oftenencountered in the field of VLSI design and validation. Using techniquesalready developed, a mapping of resistance values to i/o vectorresistance values can be developed which would allow fast and effectivereading of strain at every segment of the parachute canopy surface whichis traversed by a conductive gel segment. With this method resolutionsbetter than 1 square cm could be achieved.

Retrieving Data

Because metal gel acts exactly as a metal, electrical signals can betransmitted out either through a wired connection made of a metal geltrace running down a suspension line, or via broadcast. Each gore couldhave sewn on a small embedded system which reads out resistor values andfeeds them into a standard broadcast format. These signals could be fedinto metal gel antennas printed on the canopy surface (see FIG. 9). Theantennas can be stretched, changing its operating frequency, howeversuch changes are linear and can be matched for. A pattern of antennasbroadcasting unique ID's could also provide low resolution strain mapsof the canopy surface.

In any of the above methods strain would be measured directly on thecanopy surface, without the need for external sources of illumination orremote detection. This would enable not only high resolution measurementof the strain field without the computational overhead of imageprocessing, but also field deployable systems that would not besensitive to variable light levels, adverse weather or payload/canopymisalignment.

Validation Current Metal Gel Patterning and Encapsulation Techniques forParachute Canopy Fabric.

The objective is to adhere to the nylon material of a parachute canopy.It is not anticipated that a thin TPU trace or silicone adhesive willnegatively affect the underlying material. However tensile strength andfatigue tests are done to ensure there is no negative effect. Assessmentis performed for direct application of silicone based adhesives, such asDow Corning 7091 to parachute fabric and subsequent patterning of metalgel onto the cured sealant and adhesion of TPU encapsulated metal geltraces to the canopy fabric.

Characterization of Metal Gel Traces on Parachute Canopy Fabric

Strain testing on encapsulated metal gel traces to parachute fabric isperformed to measure strain resistance feedback relationship in weft andweave directions. A variety of standard trace patterns in weave and weftorientations will be measured through the desired strain ranges of0.2-25%. Characterized eutectic metal gel variable resistor values willbe used.

Use Output of Characterization to Model 2 Dimensional Variable ResistorStrain Sensing

Using commercial simulation tools such as MatLab and LabView multiple 2dimensional strain gauge topologies will be modeled. Of particularinterest are variable resistor mesh networks. By simulating thesenetworks with real values derived as described below will generate amapping of the high dimensional surface network of coupled linearvariable resistors to an output vector that can take on a continuousrange of values. Such a mapping will be stored in a lookup table thatcan be used for interpreting variable resistor network outputs in largerscale experimentation.

Characterize Small Scale Parachute with Variable Resistor Topology inWind Tunnel

A small scale parachute, single gored and under 3 feet, will bepatterned with two eutectic metal gel strain sensors, one for weftdirection and one for weave. System will be deployed in a wind tunneland results characterized.

Iteration of Wind Tunnel Testing with Increasing Sensor Resolution.

Increasingly high resolution sensing networks on a simple parachute willbe built, tested and validated with earlier tests. Data from strainsensor canopies will be used to validate output data from a four sensortest, which will in turn be used to validate data from incrementallymore complex and high resolution patterns.

Validate Current Metal Gel Patterning and Encapsulation Techniques forParachute Canopy Fabric

Variable resistor traces will be prepared inside TPU films. We willadhere these films to swatches of parachute canopy material measuringapproximately one foot by three inches. In addition, Silicone adhesive,such as Dow Corning 7091 adhesive/sealant will be directly applied toparachute canopy, metal gel will be patterned onto the adhesive and asecond encapsulating layer will be laid down. The output of this taskwill be best practices for depositing metal gel on parachute canopymaterial.

Characterization of Metal Gel Traces on Parachute Canopy Fabric

The above prepared swatches will be fatigued for 350 cycles and strainedto failure in an Instron 3365. Results will be compared to controlswatches of canopy fabric without metal gel traces in order to assurethat the canopy fabric is not adversely affected . On conclusion ofthese tests more involved characterization of strain/resistancerelationships will be done for different trace geometries. We willcharacterize the Gauge Factor (GF), for a L_(s)=0.5 Meter swatch ofcanopy fabric with integrated metal gel trace in both the weft and weavedirection by measuring normalized change in resistance ΔR_(s)/R_(s)versus strain, ε=ΔL_(s)/L_(s), where:

${GF} = \frac{\frac{\Delta \; R_{S}}{R_{SO}}}{ɛ}$

To obtain the data to compute GF, canopy material swatches withintegrated strain sensing traces will be mounted on an Instron 3365testing machine outfitted with a 2 kN Load Cell and a LVDT to measurethe displacement ΔL_(s). Quasi static strain tests will take place atstrains of 0-20% in 0.25% steps. Dynamic strain tests will be taken overthe range of 0-20% for 350 cycles on each sample. Displacement data willbe collected in Labview for all tests.

The change in resistance, ΔR_(s), is measured using a Wheatstone bridge,which generates an analog output voltage, V_(o), which is a function ofthe change in resistance at its input. In our application the input“strain” resistance is given by R_(s)=V_(s)/I_(s), where two metal gelwires' of length L_(s), have resistances R_(s1) and R_(s2). These twowires represent the two conductors in strain sensing topologies such asshown in FIG. 10A-10D. The analog output voltage, V_(o), is converted todigital data by using a National Instruments ADC (Analog to DigitalConverter) for analysis in Labview where it will be converted into R_(s)data. The ADC has a target spatial resolution sufficient to detect a0.25% change in voltage with a sampling rate of 1000 Hz. The ratio ofthe change in resistance ΔR_(s) to the nominal zero strain resistanceR_(so) divided by the strain, ε, gives GF. In practice attaching thissystem to a microcontroller will produce a real time dynamic view ofstrain during parachute deployment. During this task multiple conductivepatterns will be tested both in weft and weave orientations. Thesepatterns will include trace widths of 1-4 mm in 0.5 mm increments invarious geometries.

Construction of Gauge Factor Model for Simulation

Using the GFs measured, a simulation model will be created in eitherMatLab or LabView. This model will consist of a catalogue of variableresistors with strain percentages as the input and resistance changesappropriate to the metal gel pattern as the output. This catalogue ofknown and characterized metal gel traces will be used below.

Model Multiple 2 Dimensional Variable Resistor Strain Sensing

Using MatLab or Labview, circuit simulations will be built for varioustopologies of variable resistors. Using the catalogue of variableresistor models generated, accurate simulations of canopy fabric straincan be run by changing values on a simulated variable resistor network.Using these simulations, new topologies can be designed and tested inorder to achieve high resolution designs. Of particular interest will bevariable resistor grid patterns, as these are easy to build with a highdensity of strain sensors. However, we will not rule out otherunconnected or sparsely connected variable resistor networks for highresolution sensing. The output of this task will be a set of modeledpatterns which can be laid on prototype canopy systems.

Characterize Small Scale Parachute with Variable Resistor Topology inWind Tunnel

A small parachute will be purchased and two metal gel traces will beattached on one gore. One will be in the weft direction, one in theweave direction. These traces will be wired directly to a Wheatstonebridge to ADC circuit attached to a computer running LabView for realtime recording of strain results. The set up will then be deployed in atunnel. Real time data will be taken as the parachute is deployed in thewind tunnel.

Iteration of Wind Tunnel Testing with Increasing Sensor Resolution.

Using data collected above as validation, two additional higherresolution patterns will be tested. These patterns will be based onsimulation and will serve to validate the model. It is anticipated thatone pattern will be a grid of variable resistors with an output vectoras described in FIG. 8. The other pattern will be an unconnected networkof trace geometries spanning the parachute surface that multiply theoutput provide higher resolution by having an independent weft and weavespanning trace over multiple portions of the canopy surface withdedicated i/o lines such that deciphering strain feedback will betrivial.

Example 7 Application to a Nylon Fiber Parachute Suspension Cord

Direct application of eutectic metal gel to a nylon fiber parachutesuspension cord can be done at room temperature with no intermediarychemical processing necessary. A flexible and stretchable binding agent,such as 2 part polyurethane resin or silicone elastomer could be used topermanently encapsulate the gel against the nylon cord and prevent anydisplacement during normal handling and packing of the parachutesuspension and control line systems. It is expected that this processwill leave the ultimate tensile strength and flexibility of theparachute line unchanged.

Importantly, the amorphous metal structure of disclosed compositionsensure that when stretched or otherwise deformed there is linear andrepeatable resistance change which can be used for sensing. Whenpatterned into a standard parachute cord such as PIA-C-5040 andintegrated with a Wheatstone bridge, with an Analog to DigitalConverter, these linear and repeatable resistance changes can be used tomeasure dynamic forces and strains during parachute deployment.

Tests have been done to demonstrate the feasibility of coating an innercord from a MIL-C-5040H parachute line. The metal gel achieved goodwetting to the nylon and created a low resistance trace while addingnegligible weight.

The resistance of Liquid Wire conductors can be engineered by adjustingthickness and width to be on the order of 1 to 100 ohms per meter, whichis ideal for applications requiring resistance to be measured vs.stretch, since the resistance value is high enough to give a good signalto noise ratios in a Wheatstone bridge. Higher resistances, such as forCNT based conductive coatings, result in very small currents that areeasily corrupted by electromagnetic interference (EMI). Similarly copperhas such a low resistance value that the voltage drop over a few metersof line is too small to be practical, and also suffers from EMI issues.Typical resistance values for a line with dimensions of a MIL-C-5040Hcontrol line measuring 6 feet in length coated with metal gel arebetween 2 to 20 Ohms depending on deposition thickness.

Representative changes in conductivity can be seen in FIG. 6 which showsthe strain response for a metal gel wire encapsulated in a siliconerubber. Testing was carried out using an adjustable jig capable ofstretching the sample in 1.5 mm steps and a ESR meter to accuratelymeasure the sub 1 Ohm resistance of the sample during the quasi-staticstrain test.

Although not as conductive as copper, metal gel based conductors arestill viable for sending high speed data. Testing of flat tracesintended for clothing have shown that the material is suitable fortransmission of signals up to at least 6 GHz, allowing interconnects tobe directly incorporated into off the shelf radio frequency or microwavefrequency transmission systems. FIG. 11 shows measured insertion lossfor a 50 ohm microstrip line made of copper versus metal gel. Othersolutions using organic conductors can have several kilo-ohms ofresistance, making them impractical for carrying RF signals more than afew inches.

Testing Metal Gel Gauge Factor for Strain Sensing

The Gage Factor (GF) of a 0.5 meter nylon cord with integrated metal geltrace will be characterized for axial strain sensing. This isaccomplished by measuring the normalized change in resistance (ΔR/R)versus strain (ΔL/L).

RF Signal Carrying Capability

The goal of this objective is to test different types of transmissionlines made out of metal gel to characterize their RF signal carryingcapability. This will include controlling the transmission linecharacteristic impedance. The transmission lines will be designed to becompatible with the standard parachute line cord form factor.

Electromagnetic Interference (EMI) Shielding

To prevent EMI from being radiated by the metal gel lines (RadiatedEmission), or received by them (Radiated Susceptibility) some sort ofconductive shield will likely need to be used. This shield will surroundthe metal gel lines either completely or perhaps only partially. Theobjective is to test the feasibility of using carbon black loadedpolyurethane or silicone, or metal gel as a shielding layer laid over aninsulator coating an inner conductor, or conductors, made of metal gel.

Effect of Eutectic Metal Gel and Encapsulation on Suspension LineDurability

Parachute lines should have their flexibility and durabilitysubstantially unaltered by the addition of a eutectic metal gel.Ultimate tensile strength of the coated lines will be measured andcompared to uncoated versions. Likewise, the conductive metal gelcoating should be able to stand up to the same requirements offlexibility and durability the suspension lines are held to. For thisreason dynamic strain feedback will be tested by placing repeated strainon the line through 350 cycles. The objective is to see no failure onthe part of the conductor or the parachute suspension line.

Application of Metal Gels to PIA-C-5040 Parachute Lines

In this task known deposition techniques used for planar surfaces suchas found in clothing textiles will be applied and modified as needed tothe cylindrical surfaces of nylon inner cords from standard parachutesuspension lines. The subsequent encapsulation of the coated cords willbe done using both silicone and two part polyurethane. In addition,known methods for encapsulating metal gel in TPU films will be used tocreate large, extremely flexible, stretchable and low profile strainsensors that can be adhered to the outside of nylon control lines or inbetween core and sleeve cords in parachute suspension and control lines.This approach would have the added bonus of being applicable toparachute canopy material as well, since the same low profile TPUencapsulated interconnects could be adhered to the control lines and thecanopy. Some possible methods are shown in FIGS. 12A-12D. Afterassessing techniques it is anticipated a total of four types strainsensing parachute lines will be made: One with an un-encapsulatedcoating on all eight of the inner cords with the sheath providingencapsulation (FIG. 12B), one with two polyurethane encapsulated metalgel coated nylon inner cords providing an outgoing and return signalline (FIG. 12C), one with the same arrangement encapsulated in siliconerubber, and one with a separate TPU sensing ribbon running the length ofthe parachute line (FIG. 12D). Multiple lines of each type may be builtto facilitate testing.

Tensile Strength and Strain Range Testing

PIA-C-5040 parachute lines with integrated strain sensing traces will bemounted on an Instron 3364 testing machine outfitted with a 5 kN LoadCell and strained until their failure point. Tests will be compared tostock parachute lines without integrated strain sensing traces. Thelinear range of the strain feedback from the conductive traces will beassessed over the total elongation, from 0% to failure (anticipated at30%). Data will be generated on the impact of techniques on ultimatetensile strength of the parachute lines.

Metal Gel Gauge Factor for Strain Sensing

The goal of this task is to characterize the Gauge Factor, GF, for aL_(s)=0.5 meter nylon cord with integrated metal gel trace for strainsensing by measuring the normalized change in resistance ΔR_(s)/R_(s)versus strain, ε=ΔL_(s)/L_(s), where:

${GF} = {\frac{\frac{\Delta \; R_{S}}{R_{SO}}}{ɛ}.}$

To obtain the data to compute GF parachute lines with integrated strainsensing traces will be mounted on an Instron 3365 testing machineoutfitted with a 2 kN Load Cell and a LVDT to measure the displacementΔL_(s). Quasi static strain tests will take place at strains of 0-20% in0.25% steps. Dynamic strain tests will be taken over the range of 0-20%for 350 cycles on each sample. Displacement data will be collected inLabview for all tests. The change in resistance, ΔR_(s), is measuredusing a Wheatstone bridge, which generates an analog output voltage,V_(o), which is a function of the change in resistance at its input. Inour application the input “strain” resistance is given byR_(s)=V_(s)/I_(s) as shown in FIG. 13, where two metal gel wires' oflength L_(s), have resistances R_(s1) and R_(s2). These two wiresrepresent the two conductors in strain sensing topologies such as shownin FIGS. 12C and D. The analog output voltage, V_(o), is converted todigital data by using a National Instruments ADC (Analog to DigitalConverter) for analysis in Labview where it will be converted into R_(s)data. The ADC has a target spatial resolution sufficient to detect a0.25% change in voltage with a sampling rate of 1000 Hz. The ratio ofthe change in resistance ΔR_(s) to the nominal zero strain resistance Rso divided by the strain, ε, gives GF. In practice attaching this systemto a microcontroller will produce a real time dynamic view of strainduring parachute deployment.

RF Signal Carrying Capability.

This task will demonstrate transmission of RF signals along the metalgel strain sense lines. In FIG. 11 preliminary data show that theinsertion loss of RF signals in a microstrip line made of metal gel isnot significantly worse than copper through at least 6 GHz. We willexpand on this learning by designing transmission line structures thatare compatible with standard parachute line form factor. To allow RFsignals to be transmitted along the metal gel strain sense wires asystem as shown in FIG. 14 will be constructed. This is similar to theblock diagram in FIG. 13, except that a diplexer is added to allow thedc current Is to flow through an inductor L_(d) to allow R_(s1) andR_(s2) to be measured, while the capacitor C_(d) acts as a DC block andallow RF signals to enter the loop from an RF data source as shown. Theinductor prevents the RF signal from being short circuited, and at thefar end of the loop the RF signal exits the loop through capacitors C₁and C₂. For transmission of RF signals along an interconnect system acontrolled characteristic impedance is desired. To control the impedanceit is proposed that interconnect schemes such as those shown in FIG.15A-C be evaluated. The second design (B) uses a pair of close spacedconductors (3) to create a “twin lead” interconnect having an impedanceon the order of 100 to 300 ohms. The exact impedance is a function ofthe metal gel dimensions, the spacing the lines, and the dielectricconstant of the encapsulation material. The third design (C) is similarto (B), except that outer shield (4) is added to allow lower impedancevalues and reduce radiation and EMI. Test structures will be simulatedand measured to characterize their insertion loss and characteristicimpedance versus frequency. Results of the simulation and finishedtransmission line design will be the output of this task.

EMI Shielding

A proof of concept transmission line, or lines, will be fabricated inwhich a signal line will be jacketed in an envelope of conductivematerial impregnated rubber in order to provide EMI shielding, such asshown in FIGS. 15A and C. The feasibility of using carbon black loadedpolyurethane or silicone will be tested, as well as a shielding layer ofmetal gel laid over an insulating encapsulation coating an inner layerof sensing/transmission gel. Simulations will be performed using a 3Delectromagnetic simulator such as ANSYS HFSS to model the behavior. Datafrom the simulations and prototype lines will be the output of thistask.

Embedded System Design

A prototype embedded system will be designed and built for reading outvariable resistor values and converting them to strain percentages whichcan be sent out via SPI or I2C for processing elsewhere. A Wheatstonebridge designed to produce variable voltage ranging from 250 mV to 2500mV will be integrated onto a board with a 12 bit ADC, a low powermicrocontroller and a power supply. Design and construction of aprototype board does not involve any unknown science or novelengineering and should take approximately two months, depending onturnaround with an assembly contractor. Programming of the embeddedsystem is expected to take another month. Raw voltage values from theWheatstone bridge read through the ADC will need to be converted tostrain percentages based on experiments run which will have provided theappropriate GF. A less certain challenge will be the packaging designfor robustly interfacing metal gel conductors with contacts on theboard. The conductive line running the length of the parachute cord willneed to be contacted with a solid metal in such a way that the metal geltrace remains hermetically sealed so as to prevent displacement orcontamination of the metal gel. We view the most likely packaging methodto succeed will be splicing brass wires into the variable resistancetransmission lines at their terminus, sealing the junction with apotting agent and then soldering the wires into terminals on the PCB. Byusing wires of sufficient length to have some slack, and sewing theminto a ripstop fabric at the parachute suspension line terminus webelieve enough strain can be limited from the junction to allow it tooperate through multiple deployments. The finished system can bevalidated by mounting the parachute line in the Instron 3364 andimposing precise and known strains upon the line while reading data outof the embedded system. The outcome of this task will be a finishedprototype of a parachute suspension line with metal gel enabled strainsensing attached to an embedded system which can generate data out inthe form of strain percentage over either SPI or I2C data lines.

EMI Shielding Prototyping and Testing

Prototype lines consisting of a shielding layer of either metal gel orcarbon black impregnated elastomer and of sensing/transmission gel so asto create a coaxial cable or shielded bifilar line, as shown in FIGS.15A and C respectively, will be physically tested. Both systems will betested as transmission lines and their radiated emissions will be testedeither by using the anechoic chamber.

By their very nature the strain gauges shown in FIGS. 13 and 14 may havesome immunity to EMI if the two interconnects are in close proximity,such as shown in FIGS. 12C and D. This is because closely spacedinterconnects tend to experience the same electromagnetic interferenceresulting in “common mode” noise. The current flows in oppositedirections in each interconnect so the circuit operates in a“differential mode.” This means that the common mode noise currentscancel at the Wheatstone bridge input. Further immunity to EMI can beachieved by adding an outer conductor such as show in FIGS. 15A and C.

Sensing Applications of Deformable Conductors

With conventional systems, it is difficult to measure the compression ofarbitrarily shaped compressive materials such as air balloons/pockets,compressible gel or foam cushions, or other soft goods. Many systems forperforming compression measurements are intrusive and change thefundamental function of the compressive system. For example, in a systemin which biofeedback is needed, or it is desired to measure thecompression of an item vis a vis a body—such as in the case of awearable object like a shoe, a brace or some article of clothing—it isnot currently possible to have a testing apparatus in situ while theobject is being used as intended.

Likewise, in a complex system with multiple constituent parts such as ashoe, a tire, or a gasketed joint in a machine or piping system or othersuch apparatus, it may be possible to measure compressive or otherstrain response performance of certain parts of the apparatus inisolation with specialized testing equipment. However, it is verydifficult to measure the holistic performance of the apparatus wherecompressive or other strains upon the part in question are affected bythe apparatus as a whole, rather than a separate piece of testequipment. In such a case a non-intrusive and in situ measurement devicewould be desirable.

Some of the inventive principles of this patent disclosure relate to theuse of deformable conductors to electrically sense deformations in anelastic or soft material or composite object made of multiple materialsany one of which may be expected to compress, stretch, experience shearor otherwise deform. An embodiment of a sensing system according to theinventive principles of this patent disclosure may include two parts:the material of which the compression, elongation, shear or otherdeformation is to be sensed; and a patterned stretchable/flexibleconductor which does not appreciably affect the material properties ofits substrate and along which electrical signals can be sent. Bypatterning the conductor into particular geometries on the material andattaching it to a source of electric power or signals, characteristicelectrical properties, such as capacitance, inductance or impedance maybe utilized to sense the deformation of the material. Because theconductor is deformable, e.g., flexible, stretchable, etc., it can berepeatedly deformed in such as a way that the above characteristicelectrical properties change in a manner which may typically be linearand a predictable function of the deformation. Such deformable circuitswith preferably linearly changing characteristic electrical propertiescan be implemented with multiple differing geometries which performsubstantially similar end functions by differing electrical means.

Inductive sensing: in some embodiments according to the inventiveprinciples of this patent disclosure, a compression sensor may includetwo opposed inductive coils, one on either side of the material wherecompression is expected. Their mutual inductance can be measured withexternal circuitry and change as they are moved closer to one anotherdue to compression. An array of such coils may be arranged to provide aview of a compression field.

Capacitive sensing: in some embodiments according to the inventiveprinciples of this patent disclosure, two parallel plates of conductivematerial may be patterned in a geometry such that a change incapacitance is different for a shear or a compression force. Forexample, two parallel plates shaped as Ts which directly overlapexperience a large change in capacitance as shear is applied parallelwith either stem of the T but experience a relatively small change incapacitance if compressed so that the two opposing T's are broughtcloser together. By varying the widths of the stems it is possible todistinguish shear in either direction of the plain in which the patternis embedded. Specialized geometries may provide optimum performance ondiffering surfaces or be particularly sensitive to particular patternsof strain and shear.

Impedance sensing: in some embodiments according to the inventiveprinciples of this patent disclosure, an AC or RF signal sent alongpatterns of deformable conductors may be utilized to measure changes inthe characteristic impedance, frequency response, etc., of atransmission line, antenna, or other device fabricated from thedeformable conductors, thereby providing information on the deformation.The measurements may be obtained through direct reading of an electricalline, through reading the near field radiated by an electrically activepattern, by measuring the far field radiated by an electrically activepattern, etc.

Inductive pattern sensing: in some embodiments according to theinventive principles of this patent disclosure, a system for sensingcompression/shear/strain or other deformation can include individuallyaddressable inductive spiral pairs separated by a gap of deformablematerial and transmitting a unique ID via short range wireless signals(e.g., near field communication NFC)). By triangulating the signals overthe grid of inductive traces a very high resolution image of deformationcan be made.

An array of inductive coils or other radiating patterns may act as shortrange wireless devices or in a manner similar to RFID antennas. Suchpatterns may be powered by an external field, allowing them to operatewithout a local power source. Likewise, such a field may be“illuminated” by a broadcasting antenna or other EMF source and thereflected near or far field signals may be detected by an externaldevice. In such a way compression or other strain sensing patterns maybe incorporated directly into an object without the need for aninterconnect which may negatively affect the performance of the object.Such a pattern may be an antenna operating in microwave or other radiofrequency bands.

FIG. 16 is a cross-sectional view illustrating an embodiment of a devicefor capacitively sensing shear according to the inventive principles ofthis patent disclosure. The embodiment of FIG. 16 includes an elasticsubstrate A shown in the undeformed state at the top of the drawing. Afloating transmission line B made from a deformable conductor ispatterned on one side of the substrate, and a fixed in place returnline/ground C is made from a deformable conductor is patterned on theopposite side of the substrate. In this example, the substrate in therelaxed state may have a thickness H_(A1) of about 1/16th inch and widthW_(A1) of about one inch, but other dimensions may be used. The overlapbetween the two conductors creates an E-field region D having a heightH_(D1) and width W_(D1) when the substrate is in the relaxed state.Thus, the capacitance between the floating transmission line B and thereturn line C is determined by the height H_(D1) and width W_(D1) of theregion D as well as the dielectric constant of the substrate.

When the substrate A is subjected to a shear force as shown by thearrow, it deforms in such a way that the overlap between the floatingtransmission line B and the return line C increases, thereby causing thewidth of the E-field region D to increase from W_(D1) to W_(D2).Depending on the amount of shear, the height of the substrate A may alsodecrease to H_(A2), thereby causing the height of region D to decreasefrom H_(D1) to H_(D2). This change in the geometry of the E-field regionD causes an increase in the capacitance between the floatingtransmission line B and the return line C which may be sensed by anysuitable electronics, thereby enabling the embodiment of FIG. 16 tofunction as a shear sensor.

FIG. 17 is a cross-sectional view illustrating an embodiment of a devicefor sensing deformation using changes in characteristic impedanceaccording to the inventive principles of this patent disclosure. Theembodiment of FIG. 17 includes a dielectric gel sandwiched between twopieces of fabric, one of which may be attached to a fixed surface, andother of which may be attached to an adhesive or grippy surface. Tracesmade from metal gel other deformable conductor are patterned on bothpieces of fabric such that they form a transmission line having acharacteristic impedance Z₀. Each trace has an inductance L, and theyform a mutual capacitance C. The inductances and capacitance aredetermined by the geometry of the traces and gel, as well as thedielectric constant of the gel. Deformations in the structure caused bycompression, shear, etc., cause corresponding changes in the impedanceZ₀ which may be sensed by electronics, thereby enabling the embodimentof FIG. 16 to function as a deformation sensor.

FIG. 18 is a plan view illustrating an embodiment of a device forcapacitively sensing compression at various points of an array accordingto the inventive principles of this patent disclosure. The embodiment ofFIG. 18 includes a grid array having horizontal traces 102 made from adeformable conductor patterned on a top surface of a soft elastomericsubstrate 100 and vertical traces 104 made from a deformable conductorpatterned on the opposite (bottom) surface of the substrate 100.Capacitive “pixels” 106 are formed by overlapping conductors at theintersections of the top and bottom traces. When a portion of the arrayis pressed, for example by a user's finger, the capacitance of thepixels in the pressed portion increases. Electronics 108 and 110 apply asuitable stimulus and decode and sense the capacitance of the pixels,thereby enabling detection of the location of the pressing action.

FIG. 19 is a plan view illustrating an embodiment of a device forinductive sensing according to the inventive principles of this patentdisclosure. The embodiment of FIG. 19 includes an array of inductivecoils 114 made from a deformable conductor patterned on one side of asoft elastomer substrate 112. Suitable electronics may be coupled to theinductive coils to measure their self inductances, or their inductancesor characteristic impedances relative to a ground plane or other coilsthat may be formed on the other side of the substrate. When thesubstrate is pressed or otherwise deformed, it causes a change in theinductance or impedance that may be used to corresponding deformation.

The deformation sensing systems described herein may be utilized withany suitable type of deformable conductor. This includes the gallium,gallium-indium gallium-indium-tin, etc., metal gels described above.However, the inventive principles relating to deformation sensingsystems may also be realized with other deformable conductors includingionic fluids, conductive polymers, metal impregnated elastomers, carbonbased conductors including those using graphene, carbon nanotube orother allotropes of carbon, mercury or mercury amalgams, etc.

Multiplexed Applications of Deformable Conductors

Some of the inventive principles of this patent disclosure relate to theuse of multiplexing to perform multiple functions with a deformableconductor. One type of such a multiplexed system may include adeformable conductor and accompanying circuitry in which the deformationof the conductor causes a change in electrical signal properties ofvarying magnitude in one or more frequency domains which can be readseparately due to the diplexing circuit. An example of such a system isdescribed above with respect to the strain sensing and signaltransmission system of FIG. 14 in which a DC signal is changed due toelongation of a deformable conductor which increases the resistance ofthe conductor. The change in resistance is detected by means of avoltage change using a Wheatstone bridge. Simultaneously, the diplexercircuit enables a high frequency RF signal to be sent along theconducting geometry for the purposes of data transmission. In thismanner the traces fabricated from a deformable conductor may be used asboth a transmission line and a strain feedback line.

In another type of multiplexed system, a deformable conductor such as atransmission line carrying an AC signal experiences a change inimpedance when deformed. These impedance changes may be a function of ACcurrent frequency. A diplexing circuit attached to the deforming circuitenables a high frequency signal and a low frequency signal may be sentover the deforming portion of the circuit simultaneously. One of thesignals may be used to detect deformations and provide input to anactive circuit which may dynamically tune the second frequency to matchthe deformations for purposes of transmitting maximum power or someother desirable end goal in the circuit.

In another example embodiment, a multiplexed system may act as both atransmission line and a sensing line in a deformable electronic devicesuch as a robot component where it may function as both a ‘nerve’ (e.g.,for transmitting information from a sensor to a processor or fortransmitting instructions from a processor to an actuator) and as asensor itself (e.g., for detecting degree of bend in an actuatingelement or for detecting a deforming force such as a pressure or shear).

In another example embodiment, a multiplexed elastic/fluid conductor mayact as a sensor through its deformations in a soft good such as anarticle of clothing or upholstered furniture to provide biofeedback orother information about a user's body position, motion, etc., while alsoproviding electrical functions such as transmitting power to peripheraldevices, heating, signal transmission to external or internal data portssuch as I2C, USB, SPI or any other current or future standard.

As a further example, in the same type of soft good the multiplexedelastic/fluid conductor may provide feedback on deformation forbiofeedback or other purposes while being used to transmit RF datathrough antennas or transmission lines operating in the radio ormicrowave frequency range or while being used as wireless powertransmission elements or as NFC communication and power transmissionelements. A specific, but not limiting, example is an RFID tag which canbe used to transmit information about a soft good article at an RFfrequency while also acting as a pressure sensor under DC as itsresistance appreciably changes due to deflection of the antenna tracepattern on a soft substrate when pushed. An RFID, NFC or Wirelesscharger may be activated for AC transmission through circuitry activatedby means of a conductivity or impedance change at a DC ornon-characteristic AC frequency due to deformation of the elastic/fluidconductor pattern.

Referring again to the multiplexed strain sensing and signaltransmission system of FIG. 14, an example application of this type ofsystem is shown in FIG. 20 which illustrates an embodiment of a straincontrolled oscillator that uses deformable conductors that function asboth a strain sensor and transmission line according to some inventiveprinciples of this patent disclosure. In the embodiment of FIG. 20, thestrain sensor is fabricated from two parallel deformable conductorsshown as resistors R_(S1) and R_(S2), each having a length L_(S). Adiplexer includes an inductor L_(d) which provides a DC current path fora sense current I_(S) so resistors R_(S1) and R_(S2) are effectivelyconnected in series for DC currents. The diplexer also includes an ACcoupling (DC blocking) capacitor Cd that prevents the DC current I_(S)from being coupled to antenna 124.

As the strain sensor is stretched, the resistances R_(S1) and R_(S2)increase in relation to the amount of stretch. A resistive bridge 120,which may be implemented as a Wheatstone bridge for example, senses thechange in the resistances R_(S1) and R_(S2) by sensing the change involtage at nodes a and b and/or the change in sense current I_(S), andconverts this change in resistance to a change in output voltage V_(o),which is then fed as the input tuning voltage V_tune to a voltagecontrolled oscillator (VCO) 122. The frequency of the RF output signalfrom the VCO is proportional to V_(o), which is also proportional to thecombined resistance of R_(S1) and R_(S2) and thus, is proportional tothe length L_(S) of the strain sensor. The RF output signal from the VCOis coupled to the strain sense lines through DC blocking capacitors C₁and C₂ which prevent the RF signal from affecting the resistive bridge120. The RF signal then propagates down the transmission line formed bythe deformable conductors and is coupled at nodes c and d to the antenna124 through the AC coupling capacitor Cd. The antenna thus radiates anRF signal at a frequency that is determined by length L_(S) of the senselines R_(S1) and R_(S2). The radiated RF signal may be received with anysuitable antenna and receiver and converted to strain data withmicroprocessor and/or any suitable apparatus arranged to operate as afrequency counter.

The multiplexed systems described herein may be utilized with anysuitable type of deformable conductor. This includes the gallium,gallium-indium gallium-indium-tin, etc., metal gels described above.These metal compositions have conductivities on the order of 10̂5-10̂6Siemens/Meter which allow for signal transmission rates up to theMHz-GHz range over meters of distance while also providing linear strainfeedback through resistance or inductance changes when deformed.However, the inventive principles relating to multiplexed systems mayalso be realized with other deformable conductors including ionicfluids, conductive polymers, metal impregnated elastomers, carbon basedconductors including those using graphene, carbon nanotube or otherallotropes of carbon, mercury or mercury amalgams, etc.

FIG. 21 is a cross-sectional view of a transmission line structuresuitable for use with deformable conductors according to some inventiveprinciples of this patent disclosure. The structure of FIG. 21 utilizesa slot-line structure and includes a signal line trace and a ground linetrace patterned on a stretchable substrate and separated by a gap. Inthis example, the substrate may be ¼ inch thick silicon with dielectricconstant of about 2.9. The entire structure may be encapsulated inanother layer of silicon. This type of transmission line tends to haverelatively unconstrained field lines and is difficult to achieve lowimpendences with. However, its simplicity typically makes it lessexpensive to fabricate so it would be advantageous to find a techniqueto use a slot line structure with deformable conductors on anstretchable substrate. The embodiment of FIG. 22 achieves thisobjective.

FIG. 22 is a plan view illustrating an embodiment of a diplexed strainsensor similar that of FIG. 20 fabricated using the slot line structureof FIG. 21 for the strain measuring resistances R_(S1) and R_(S2). Nodesa, b, c and d in FIG. 22 correspond to the same nodes in FIG. 20. Theantenna 124 is implemented as a folded dipole with inductive coupling.The entire structure is made with deformable conductors patterned on anelastomeric substrate. The elements illustrated in FIG. 22 are not shownto scale and may have exaggerated dimensions and proportions forpurposes of illustration. The diplexer is implemented with a surfacemount inductor L_(d) and a surface mount capacitor C_(d). The inductorL_(d) is connected across the Signal and Ground traces at nodes c and d,while the capacitor C_(d) is connected across a gap in the primary traceof the antenna. The surface mount components my be encapsulated in aless deformable material to prevent them from pulling away from thedeformable conductors. Alternatively, a specially woven fabric or otherless deformable material may be attached to the substrate under theinductor and capacitor to preserve the integrity of the electricalconnection during deformation.

The embodiment of FIG. 22 may provide an effect low-cost implementationthat may be especially suitable for use in where relatively highertransmission line impedances are used, for example, with dipole antennashaving impedances above about 70 ohms.

FIG. 23 is a cross-sectional view of another transmission line structuresuitable for use with deformable conductors according to some inventiveprinciples of this patent disclosure. The structure of FIG. 23 utilizesa coplanar waveguide (CPW) structure that typically has more constrainedfield lines and may achieve lower impedances through the use of abalanced (differential) structure that uses two separate ground traces.

FIG. 24 is a plan view illustrating another embodiment of a diplexedstrain sensor similar that of FIG. 20 fabricated using the coplanarwaveguide structure of FIG. 23 for the strain measuring resistancesR_(S1) and R_(S2). In this embodiment, the dual Ground traces result innodes b′ and d′ that perform a similar function to nodes b and d,respectively. Because of the differential structure, the inductor L_(d)is now split into two separate inductors L_(d1) and L_(d2). TheWheatstone bridge, VCO and other electronics are fabricated as a surfacemount component 128 that may be mounted in the gap between traces andcoupled to the deformable conductive traces in the same manner as theother surface mount components, L_(c1), L_(d2) and C_(d). Theelectronics component 128 may also be encapsulated or otherwiseprotected from pulling away from the conductors as described above.

To accommodate the symmetry of the CPW transmission line, the antenna isfabricated on a separate layer from the other components andcapacitively coupled to the transmission line through pads 126 a and 126b which are shown in dashed lines to indicate that they are locatedbeneath the antenna and separated by an insulating layer.

The antenna is implemented as a bow tie antenna for widebandperformance, and each half of the antenna has a pad that is positionedover the corresponding pad that is coupled to the diplexer. The elementsillustrated in FIG. 24 are not shown to scale and may have exaggerateddimensions and proportions for purposes of illustration. The embodimentof FIG. 24 may provide a high performance implementation that may beespecially suitable for use in where relatively lower transmission lineimpedances are used, for example in applications where a 50 ohmtransmission line is beneficial.

As discussed above, e.g., with respect to FIG. 9, deformable conductorsformulated according to the inventive principles of this patentdisclosure may enable the fabrication of antennas that retain theirfunction even when subjected to large deformations. FIG. 25 illustratesthe return loss versus stretch for a bow tie antenna fabricated withmetal gel according to the inventive principles of this patentdisclosure. The right trace shows the return loss as a function offrequency when the antenna is in the relaxed (undeformed) state, whilethe left trace shows the return loss as a function of frequency when theantenna is stretched 25 percent. As can be seen from FIG. 25, the returnloss is better than 10 dB (i.e., less than ten percent of the incidentpower is reflected) over a 250 MHz bandwidth even when the antenna isstretched between zero and 25 percent. The approximate geometry of thetested antenna is shown in FIG. 26.

Since the inventive principles of this patent disclosure can be modifiedin arrangement and detail without departing from the inventive concepts,such changes and modifications are considered to fall within the scopeof the following claims.

1. A conducting shear thinning gel composition, comprising: a eutecticgallium alloy; and gallium oxide sheets distributed as microstructureswithin the gallium alloy, wherein the mixture of eutectic gallium alloyand gallium oxide has a weight percentage (wt %) of between about 59.9%and about 99.9% eutectic gallium alloy, and a wt % of between about 0.1%and about 2.0% gallium oxide.
 2. The conducting shear thinning gelcomposition of claim 1, further comprising one or more micro-particlesor sub-micron scale particles dispersed within the mixture, where themicro-particles have a wt % of between about 0.001% and about 40.0% ofmicro-particles in the composition.
 3. A method of making a conductingshear thinning gel composition, comprising: blending surface galliumoxides formed on a surface of a gallium alloy fluid into the bulk of thegallium alloy fluid by shear mixing of the surface oxide/alloyinterface; and inducing a cross linked microstructure in the surfaceoxides; thereby forming a conducting shear thinning gel composition. 4.The method of claim 3, a mixture of a eutectic gallium alloy and galliumoxide, wherein the mixture of eutectic gallium alloy and gallium oxidehas a weight percentage (wt %) of between about 59.9% and about 99.9%eutectic gallium alloy, a wt % of between about 0.1% and about 2.0%gallium oxide.
 1. A conducting shear thinning gel composition,comprising: a eutectic gallium alloy; and gallium oxide sheetsdistributed as microstructures within the gallium alloy, wherein themixture of eutectic gallium alloy and gallium oxide has a weightpercentage (wt %) of between about 59.9% and about 99.9% eutecticgallium alloy, and a wt % of between about 0.1% and about 2.0% galliumoxide.
 2. The conducting shear thinning gel composition of claim 1,further comprising one or more micro-particles or sub-micron scaleparticles dispersed within the mixture, where the micro-particles have awt % of between about 0.001% and about 40.0% of micro-particles in thecomposition.
 3. A method of making a conducting shear thinning gelcomposition, comprising: blending surface gallium oxides formed on asurface of a gallium alloy fluid into the bulk of the gallium alloyfluid by shear mixing of the surface oxide/alloy interface; and inducinga cross linked microstructure in the surface oxides; thereby forming aconducting shear thinning gel composition.
 4. The method of claim 3, amixture of a eutectic gallium alloy and gallium oxide, wherein themixture of eutectic gallium alloy and gallium oxide has a weightpercentage (wt %) of between about 59.9% and about 99.9% eutecticgallium alloy, a wt % of between about 0.1% and about 2.0% galliumoxide.